When it comes to large machines of this type, particularly for generating electricity in a power plant, the stator has a winding made up of several winding bars. These winding bars, which are preferably configured as so-called Roebel bars, extend in the axial direction in a stator core. At least on one axial face of this stator core, the ends of the winding bars protrude out of the stator core. Normally, the protruding ends of the winding bars are bent and arranged in such a way that, on the core face, they form a truncated winding head whose cross section increases as the distance from the core face increases.
Normally, the stator winding of the electric machine is fitted with several terminals so that electric energy can be fed into and/or dissipated out of the stator winding, depending on whether the electric machine is configured or operated as an electric motor or as a generator. For this purpose, selected winding bars, so-called phase-winding bars, have to be connected to these terminals. This can be done, for instance, by means of phase connector bars, each of which connects one of the phase-winding bars in the area of the core face to one of the terminals.
As a rule, the phase connector bars extend between their ends in a ring segment manner along the circumference of the stator, whereby they rest internally and radially on one or more supports distributed in the area of the core face along the circumference. These supports can be provided with two stationary axial stops between which there is at least one phase-connector bar. Normally, there are several phase connector bars between the axial stops of the supports. Advantageously, spacers with which the phase connector bars come into axial contact are arranged between each of the adjacent phase connector bars in the area of the supports. Here, each of the phase connector bars located axially on the outside can either be in direct contact with the axial stop facing them or else, via another spacer, they can each be in indirect contact with the axial stop facing them. The spacers are advantageously dimensioned in such a way that, after the assembly, a press fit is created in the axial direction for the phase connector bars located between the axial stops. As a result, the phase connector bars are effectively affixed to the supports, which is necessary in view of the loads that occur during the operation of the electric machine.
As a rule, the outside of the phase connector bars are provided with insulation, normally a synthetic resin. When the resin hardens and due to the heat that is generated during the operation of the electric machines, settling phenomena can occur which can cause the insulation of the phase connector bars to yield slightly in the axial direction. As a result, the axial pressing in the press fit between the axial stops of the supports drops markedly which, during the continuous operation of the machine in question, can reduce the axial holding forces to such an extent that the spacers can move relative to the phase connector bars due to the occurring vibrations. This gives rise to abrasive effects, thus causing the destruction of the electric insulation of the phase connector bars. Moreover, under certain circumstances, the spacers can become completely detached and fall out, thereby rendering the axial holding of the phase connector bars unstable. These processes entail an undesired risk potential and require regular inspections and at times complex maintenance measures.